Optical Coherence Tomography (OCT) incorporates well known optical techniques for creating images of objects in various environments. Of particular interest here are images of different anatomical structures inside an eye. For example, insofar as ophthalmic laser procedures are concerned, OCT has been effectively used for establishing the structural relationships that anatomically exist between optical elements inside the eye, such as the cornea, the anterior chamber, the crystalline lens, the vitreous and the retina. In this context, OCT has been particularly effective when used to establish a reference datum in the eye that can be used for the guidance and control of a laser focal point during ophthalmic surgery. It will be appreciated by the skilled artisan that imaging techniques other than OCT may be used where appropriate. For example, techniques such as Scheimpflug imaging, confocal imaging, optical range finding, two-photon imaging or acoustical (non-optical) imaging may be useful.
As will be readily appreciated, in an ophthalmic surgical procedure, precision and accuracy in the placement and movement of a laser beam's focal point are of utmost importance. In particular, this precision and accuracy are important in situations (procedures) wherein the placement of a laser beam's focal point must be accurate to within tolerances as small as plus or minus five microns (±5 μm). The situation can be complicated, however, when optical materials (e.g. an Intraocular Lens (IOL) or inlays such as corneal inlays) are implanted into the eye, and are located on the optical path of the laser beam. In such a situation, the holographic, accommodating or refractive/diffractive changes that are introduced into the optical path by the implant material may have an untracked effect on the placement of the focal point. Stated differently, an intended focal point location (as might be established using imaging techniques) may be changed by the implant material such that the actual focal point location is not as intended. Such a deviation in focal point location is particularly problematic when very small tolerances are required for focal point placement, and the deviation is also very small.
By way of example, consider the situation presented by Posterior Capsule Opacity (PCO). The problem presented by PCO after a cataract surgery is that biological growths will sometimes intrude into the space between the posterior surface of an IOL and the posterior capsule. A consequence here is that the patient's vision deteriorates and becomes hazy. To correct this, it is envisioned that lasers can be used to ablate or remove these biological growths. It happens that the space where these biological growths are located, i.e. in the optical zone between the posterior surface of an IOL and the posterior capsule, is very small. Moreover, it is important that the IOL not be damaged during the removal of the offending biological growth.
In light of the above, it is an object of the present invention to provide a method for correcting the placement of a laser beam's focal point to compensate for displacements of the focal point caused by implant material positioned on an optical path of the laser beam. Another object of the present invention is to provide a method for augmenting OCT or other imaging capabilities for use in the guidance and control of a laser beam's focal point. Still another object of the present invention is to provide a methodology for treating ophthalmic conditions behind implant material deep in an eye (e.g. crystalline lens, vitreous or retina) which is simple to implement, is easy to use and is comparatively cost effective.